1. Field of the Invention
This invention relates to display devices and, more particularly, to electrochromic devices.
2. Art Background
Electrochromic cells are actively being investigated for use as display devices. Most of this investigative effort has involved devices utilizing WO.sub.3. Recently iridium oxide has been suggested as a viable alternative to the established WO.sub.3 containing cell. These cells are fabricated by immersing an electrochromic iridium oxide electrode in an aqueous electrolyte. Both acidic and basic electrolytes are useful and yield a long term memory with extremely good response times, e.g., 50 milliseconds for an optical reflectance change of 50%. The mechanism in iridium oxide cells leading to the electrochromic behavior has engendered considerable controversy. (See S. Gottesfeld and J. D. E. McIntyre, Journal of the Electrochemical Society, 126, 742, [1979], and G. Beni and J. L. Shay, Applied Physics Letters, 33, 208 [1978].) For example, these proposed mechanisms are based on either proton or electron exchange between the electrolyte and the electrochromic iridium oxide electrode to produce charge neutrality. That is, it is postulated in these mechanisms that during coloration either a proton is ejected or an electron is injected to compensate for the electron extracted by the potential applied to the electrode to change its reflectivity.